Rare is the issue that brings Iran, Iraq, Turkey and the U.S. all to the same side, but the question of independence for the Kurdish people seems to have done it.

Today the semi-autonomous region of Kurdistan in northern Iraq is holding an advisory referendum on whether it should be fully independent. It's a vote that regional powers vehemently did not want to happen and that the U.S. contested as a distraction.

The Kurds are the largest ethnic group in the world without a home state, with an estimated population between 25 and 35 million spread between Turkey, Iraq, Iran, Syria and Armenia. (If the higher-end figure is correct, that's nearly the population of Canada, according to the World Bank.)

U.S. military officials have praised the Kurdish forces for their effectiveness in confronting ISIS in Iraq and Syria, and it's long been suspected that the Kurds would use their resurgent strength and battlefield territorial gains for a renewed push for independence.

"The independence of Kurdistan is the right of our people," Nechirvan Barzani, the Iraqi Kurdish regional prime minister, told Voice of America in July 2016. "Choosing our destiny is a legitimate right and will remain a goal for us and all the Kurdish people. What is important for us after Daesh [ISIS] is Kurdistan's borders. We will decide the extent of our borders by what has been liberated with the blood of our Peshmerga [Kurdish fighters]."

But others in the region have plenty to say about that. Last week the foreign ministries of Iran, Iraq and Turkey reportedly released a joint statement voicing their "unequivocal opposition" to the referendum and warning of unspecified "countermeasures."

Sunday Iran closed its airspace to all flights in and out of Kurdistan, which it said was done at the demand of the Iraqi government in Baghdad. According to Iran's English-language Fars News, a spokesperson for Iran's Supreme National Security Council (SNSC) said the decision was made, as the paper put it, "after the failure of Iran's good-will political efforts to convince the Iraqi Kurdistan" to drop the independence referendum.

Today Turkish leader Recep Tayyip Erdogan offered an ominous warning to the Kurdish regional government in Iraq, suggesting his military "might come suddenly one night."

A longer statement posted on the website for Turkey's Foreign Ministry says the referedum is already "null and void in terms of its consequences."

"We stress one more time that we will take every measure that emanates from the international law and from the authority granted by the Grand National Assembly of Turkey, in the event that some radical elements and terrorists, which may seek to exploit the circumstances that will emerge following the referendum, attempt to carry out acts that target our national security," the statement says.

Turkey has long-considered militant Kurdish groups in Turkey as terrorist organizations, including Turkey-PKK, which has also on the U.S. terror list for 20 years.

The situation has left the U.S., which reportedly supplied arms directly to the Kurds fighting ISIS and generally enjoys being seen as a fan of the whole "independence" thing, in a precarious position.

"[T]he U.S. government... we don’t support the planned Kurdish referendum on September 25th because we feel that that takes the eye off the ball of ISIS and that we should all remain focused on ISIS," State Department spokesperson Heather Nauert told reporters on Sept. 14. "And when I topped at the beginning of this briefing with that most recent attack that took place in Nineveh province, that’s a good reminder why we can’t take our eye off the ball, which is ISIS... Our position is firm that we don’t support this referendum at this time. We do not support the referendum on Kurdish independence at the time because of ISIS. Okay."

The referendum itself is non-binding and it's unclear what the impact of the vote will be. Russian Foreign Minister Sergey Lavrov, after artfully dodging the question of Russia's views on Kurdish independence in an interview with a Kurdish news station in July, offered this prediction:

"History shows that all too often the holding of a poll does not mean that all the issues will be resolved overnight," he said then. "These are processes which, I repeat, should be handled in a responsible manner considering the great significance of the Kurdish issue for the whole region."

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